Arsenical insecticide and method of making same



Patented Dec. 21, 1943 2,337,054 I ARSENICAL INSECTICIDE AND METHOD OF MAKING SAME John F. Les Veaux, Middleport, N. Y., assignor to Niagara Sprayer and Chemical 00., Inc Middleport, N. Y., a corporation 1 No Drawing. Application April 2,1941,

Serial No. 386,545

8 Claims.

This invention relates to arsenical insecticides and more particularly to arsenates of lead and to methods of preparing the same.

In many apple growing regions and particularly in the northwestern regions of the United States it has recently become more and more the practice in orchards suffering from unusually heavy infestations of codling moth to increase the amount of lead arsenate deposited upon a unit area of the fruit surface by means of special sprays (now generally known in the art as dynamite sprays) in the spray tank.

In earlier practice, this treatment consisted in adding three pounds of dry, powdered acid lead arsenate to each 100 gallons of water in the spray tank, then adding one quartof a suitable petroleum oil to each 100 gallons of water, the oil being first emulsified with a soap such as triethanolamine oleate. The lead arsenate reacts with the soap by double decomposition forming lead oleate resulting in the breaking up of the oil emulsion and the formation of flocks of lead arsenate coated with the lead oleate, the oil becoming tangled up with these flocks of lead arsenate and lead oleate.

When such a spray is applied to the trees by ordinary spray equipment a large portion of the lead arsenate'particles along with a portion of the oil sticks to the surface of the fruit, leaves, branches, etc., while the water runs off carrying with it the remainder of the oil and lead arsenate. Depending upon the time period duringwhich the spray is directed at a particular area, the lead arsenate deposit can be built up" in this way to extremely heavy residues of lead arsenate during a single application.

However, a serious defect of this technique is the phytocidal or injurious action upon the trees or fruit of the soluble arsenic produced in the spray. tank byv the double decompositionbe tween the lead arsenate and the soluble soap. In some apple-growing regions this spray has caused severe damage to whole orchards.

In later practice of this method attempts-were made to overcome this serious difliculty by dissolving a small amount of oleic acid in a socalled non-phytocidal oil (about 5% oleic acid plus 95% of the non-phytocidal oilworks very well), adding the oil containing the oleicacid,

without emulsification, to the water in the spray tank and then sprinkling in the lead arsenate powder and stirring. This practice is much less drastic from a. phytocidal standpoint but itwas found that for some unknown reason suchspray compositions could not be depended upon to give satisfactory resultsthat is they would not build up a satisfactory heavy deposit of lead arsenate on sprayed apples with only a minor portion of the lead arsenate being carried off with the run off" water. The results in these respects were very erratic and inconsistent.

The present invention is directed to a solution of these difficulties. In brief, I have found that the solution of this problem lies in binding or attaching a relatively small amount of basic lead arsenate to the particles of acid lead arsenate, preferably by precipitating the basic lead arsenate upon the particles of the dispersed finely divided or deflocculated acid lead arsenate in themecipitating tanks during the process of manufacture, before drying and grinding. The improved finished product thus formed, even after drying and grinding, is directly and highly reactive with the oleic acid in the oil layer floating on the water in the spray tank, producing an adherent coating of lead oleate on the lead arsenate particles which in turn is readily compatible with and wetted by the floating oil film. The net result is that the particles of the dried, pulverized lead arsenate comprising small aggregates of the coated deflocculated particles mentioned above, and composed essentially of acid lead arsenate and a slight amount of a basic lead arsenate, are always deposited on the vegetation in a smooth, complete coverage which affords maximum protection against codling moth larvae and gives a minimum of'adverse phytocidal effects because soluble arsenic is not produced in any appreciable amount by the oleic acid. I o

The following example will describe the preferred method of manufacture of my improved lead arsenate more precisely:

Into a suitable tank provided with eflicient agitator and containing 100 gallons of water at -C., I slowly sift 214.75 pounds of lead oxide (PbQTwith theagitator running. I next add 1.92 lbs. of 80% acetic acid. I then gradually add 11.65 gallons (181.9 pounds) of'l5% arsenic acid (I-IaAsO4) at a uniform rate during a period of about 30 minutes. During this operation the temperature rises to about C.

I now make cautious additions of arsenic acid in small measured quantities to the batch in the tank. After each addition I test the sludge in the tank for excess arsenic acid. The test employed is as follows: i

I dip a strip of Whatman No. 2 fllter paper r equivalent grade, out about 1" wide, intoa sample of lead arsenate sludge for a distance of about one inch; I then withdraw the filter paper, hold it horizontally and flow onto the moist portion of the filter paper adjacent to the adherent sludge, about two drops of silver nitrate solution, taking care not to allow the silver nitrate solution to come in contact with .the adherent sludge. The presence of excess arsenic acid is indicated by the formation of a red color or precipitate where the silver nitrate solution mingles with the filtrate from the sludge.

When the litharge has been completely reacted with the arsenic acid in this manner, to the point where an exceedingly slight or negligible addition of arsenic acid just produces the red precipitate in the test there is formed a sludge Of acid lead arsenate (PbHAsO4) with no appreciable excess of either arsenic acid or litharge.

' and technique described but various changes may Taking the total amountof arsenic acid added up to this point as 100% of the stoichiometric requirement for forming acid lead arsenate (PbHAsOr), there is now added to the hot batch in the tank sufiicient excess of arsenic acid to make a total of 102% of this stoichiometric requirement or a total of 1.02 moles per each mole of litharge employed. The reaction is continued to substantial completion after which the resulting reaction product or wet sludge gives a very definite red precipitate or streak" by the strip test described above due to the excess arsenic acid.

To the still hot batch in the precipitating tank is now added, with stirring, an additional 0.03 of a mole of litharge which has been previously stirred into 5 gallons of water'containing suflicient acetic acid to convert all of it into basic lead acetate. The react on under these conditions is, completed ,in a relatively short period of time as shown by the absence of any appreciable amount of soluble leadv salt in the aqueous phase or liquid. In this reaction it will be obvious, of course, that of the 0.03 mole of added litharge a certain portion or 0.02 mole is required to comarsenate leaving an excess of 0.01- mole of litharge (in the form of soluble lead acetate) which then reacts completely with the suspended particles of all of the previously formed acid lead arsenate to convert a small portion of the particles on their outer surfaces to a basic lead arsenate containing the excess 0.01 mole of litharge in combined form.

be made therein without departing from the true scope of my invention as set forth in the appended claims.

Thus, among the various changes which may be made are the following:

More or less water within wide limits may be used in the precipitating tubs.

The acid lead arsenate and the final product may be formed at temperatures varying from about 50 C. to 100 C. (o higher under pressure).

The amount of acetic acid used as catalyser may be varied widely and the acetic acid may besubstituted with equivalent amount of nitric, fluoaluminic, fiuoboric, fiuosilic, hydrofluoric or similar acids, the lead salts of which are soluble, as is well known in the art.

The excess of arsenic acid over the amount needed to form acid lead arsenate prior to the precipitation thereon of a slight amount of basic lead arsenate may be varied from substantially none to about 20%.

The time period for the first or main addition of the arsenic acid may be varied from about ten minutes to an indefinitely long period.

,The amount of excess of lead oxide used in the last precipitation step, over and above the amount required to bring the ingredients back to the proper stoichiometric proportions to form acid lead arsenate, may be varied from not less than about one tenth of one percent to about ten percent. It has been found that an excess of combined litharge above about ten percent rapidly decreases the insecticidal value of the spray to a very objectionable extent and that less than about one tenth of one percent does not produce thedesired result in actual use, i. e., the oil-oleic acid-lead arsenate spray does not consistently build up heavy, smooth residues or deposits of lead arsenate on the fruit and foliage as explained above. As previously indicated the preferred excess of combined litharge is about one percent.

As a result of the aboveprocedure the defioc- The lead arsenate sludge formed by the aboveprocedure is now separated from the liquid, dried, pulverized and packaged for field use. The pulverized product has been extensively tested by field use in combination with oil containing 5% oleic acid as described above and has never failed to produce an oil-lead arsenate dispersion that builds up heavy, smoothresidues on both fruit and leaves, thus afiording maximum protection against the ravages of codling moth larvae and being quite safe from a phytocidal standpoint.

Variations While the above method is preferred, my invention is not limited to the exact proportions Normal lead acetate or. other soluble lead salt may be substituted for the basic lead acetate.

Also uncombined powdered litharge may be substituted for lead acetate'especially at temperatures above 80 C. At lower temperatures a highly reactive litharge is necessary to complete the reaction during a practical tme period.

The improved lead arsenate of the, present invention may, if desired, or if required by law, be colored a bright pink by the use of the sodium salt of tetrabromo-fiuorescein or (czoHsBrrosNaa).

In this coloring process, this dye is added to the hot batch in the precipitating tank after the addition of the 2% or 0.02 mole excess of arsenic acid. In the above specific example the amount of dye added should be about 1.92 ounces correspending to only about 0.0002 mole.

At this stage the color produced in the slurry is an orange or a streaky orange and pink. After the addition of the final portion or 0.03 mole of litharge (dissolved in acetic acid) this orange or streaky orange and pink color changes to a bright pink due to the formation of the insoluble lead salt of the dye by double decomposition with the soluble lead salt (lead acetate), this reaction requiring equal molor weights of the dye and the dissolved litharge.

In the specific example given the amount of dye added corresponds to only 0.0002 mole but is usually suificient to impart to the final dried and powdered lead arsenate the required distinctly pink, color. It will be obvious from this that of the final portion or 0.03 mole of litharge added in the specific example to form the basic-coated acid lead arsenate suspension, the amount used up in forming the lead salt of the dye in the coloring step amounts to only 0.0002 mole and also that the final basic-coated acid lead arsenate product of the specific example will then contain an excess of 0.008 mole or 0.8% instead of 0.01 mole or 1% of combined litharge.

From the foregoing it will be clear that in preparing the colored form of the basic-coated acid lead arsenate of my invention so that it shall contain a definite predetermined excess of combined litharge, allowance should be made for the amount of the sodium salt of tetrabromofiuorescein employed, especially where the predetermined excess of combined litharge is very small, as for instance where it is near the lower limit of about 0.1% as previously explained. The manner in which this allowance may be made will be obvious from the above specific example of the coloring step.

The basic coated acid lead arsenate produced by the method of this invention is also especially well suited to those spray programs where a larger amount of oil than that specified above is desired. In this case about three quarts of oil per 100 gallons with pounds of lead arsenate are used.

The amount of oil in this case is too great to be absorbed by the lead arsenate whereby a certain degree of emulsification is produced. It

1. A powdered insoluble insecticidal compo-- sition consisting essentially of an acid arsenate of lead comprising particles ofdefiocculated dimensions, a, substantial portion of the relatively very thin peripheral layers of which consist essentially of a basic arsenate of lead, said composition being substantially free from soluble arsenical compounds and possessing, theproperty of quickly reacting with relatively small amounts of oleic acid dissolved in mineral oil when admixed therewith to coat the particles of the said composition with lead oleate whereby they become readily wetted by and dispersed in the said 011.

2. A powdered insoluble insecticidal composition consisting essentially of an acid arsenate of lead comprising particles of defiocculated dimensions, a substantial portion of the relatively very thin peripheral layers of which consist essentially of a basic arsenate of lead, said composition being substantially free from soluble arsenical compounds and possessing the property of quickly reacting with relatively small amounts of oleic acid dissolved in mineral oil when ad- However, the

3. A powdered insoluble insecticidal composition consisting essentially of an acid arsenate of lead comprising particles of defiocculated dimensions, a substantial portion of the relatively arsenical compounds and possessing the prop-.

erty of quickly reacting with relatively small amounts of oleic acid dissolved in mineral oil when admixed therewith to coat the particles of the said composition with lead oleate whereby they become readily wetted by and dispersed in the said oil, the average composition of the said insecticidal composition corresponding to about 1.01 moles of combined lead oxide per mole of acid lead arsenate. I

4. The method of making in insecticidal arsenate of lead which comprises forming a water suspension of finely divided acid arsenate of lead having a. composition corresponding substantially to the formula PbHASOd and then reacting the suspended particles of the acid lead arsenate with arelatively small amount of lead oxide in the form of a soluble lead salt, whereby the particles of acid lead arsenate become covered, over a substantial portion of their surface, with an adherent coating of a relatively small proportion of a basic arsenate of lead.

5. The method ofmaking an insecticidal arsenate of lead which comprises forming a water suspension of finely divided acid arsenate of lead having a composition corresponding substantially to the formula PbHAsO4 and then reacting the suspended particles of the acid lead arsenate with a relatively small amount of lead oxide in the form of a soluble lead salt, whereby the particles of acid lead arsenate become covered, over a substantial portion of their surface, with an adherent coating of a relatively small proportion of a basic arsenate of lead, the proportion of thelead oxide being not less than about 1.001 moles and not more than about 1.1 moles to each mole of the acid lead arsenate.

6. The method of making an insecticidal arsenate of lead which comprises forming a water suspension of finely divided acid arsenate of lead having a composition corresponding substantially to the formula PbHASO-i and then reacting the suspended particles of the acid lead arsenate with a relatively. small amount of lead oxide in the form of a soluble lead salt, whereby the particles of acid lead arsenate become covered, over a substantial portion of their surface, with an adherent coating of a relatively small proportion of a basic arsenate of lead, the proportion of the lead oxide being about 1.01 moles to each mole of the acid lead arsenate.

7. The method of making a uniformly colored bright pink insecticidal'arsenate of lead which comprises reacting finely divided. lead oxide in suspension in water witha relatively small excess of arsenic acid to form, in the water containing the slight excess of arsenic acid, a suspension of finely divided acid arsenate of lead corresponding substantially to the formula PbHASO4 and then reactingtlie mixture thus produced with an' additional quantity of lead oxide suflicient to convert the excess of arsenic acid into an additional quantity of finely divided,

suspended acid arsenate of lead and to convert a relatively small proportion of the total finely divided, suspended acid arsenate of lead thus formed into a basic arsenate of lead, whereby substantially all of the particles of acid arsenate tion of their surface, with an adherent coating of a relatively small proportion of a basic arsenate of lead.

. 8. Themethod of making a uniformly colored bright pink insecticidal arsenate of lead which comprises reacting finely divided lead oxide in suspension in water with a. relatively small excess of arsenic acid to form, in the water containing the slight excess of arsenic acid, a suspension of finely divided acid arsenate of lead corresponding substantially to the formula PbHASO4 and then reacting the mixture thus produced with an additional quantity of lead oxide sufiicient to convert the excess of arsenic of lead become covered, over a substantial poracid into an additional quantity of finely divided, suspended acid arsenate of lead and to convert a relatively small proportion of the total finely divided, suspended acid arsenate of lead thus formed into a basic arsenate of lead, whereby substantially all of the particles of acid arsenate of lead become covered, over a substantial portion of their surface, with an adherent coating of a relatively small proportion of a basic arsenate of lead, the additional amount of lead oxide employed being not less than about 1.001 moles and not more than about 1.01 moles per mole of the total acid arsenate of lead formed.

J OHN F. LES VEAUX. 

